RNA: Cleanup PointerRNA struct

The old layout of `PointerRNA` was confusing for historic reasons:
```
typedef struct PointerRNA {
  struct {
    void *data;
  } id;

  struct StructRNA *type;
  void *data;
} PointerRNA;
```

This patch updates it to:
```
typedef struct PointerRNA {
  struct ID *owner_id;
  struct StructRNA *type;
  void *data;
} PointerRNA;
```

Throughout the code base `id.data` was replaced with `owner_id`.
Furthermore, many explicit pointer type casts were added which
were implicit before. Some type casts to `ID *` were removed.

Reviewers: brecht, campbellbarton

Differential Revision: https://developer.blender.org/D5558

1 files changed, 2 insertions, 2 deletions

diff --git a/source/blender/editors/space_graph/graph_buttons.c b/source/blender/editors/space_graph/graph_buttons.c
index c727c5225c9..b264a5cb260 100644
--- a/source/blender/editors/space_graph/graph_buttons.c
+++ b/source/blender/editors/space_graph/graph_buttons.c
@@ -1236,7 +1236,7 @@ static void graph_panel_drivers_popover(const bContext *C, Panel *pa)
 {
   uiLayout *layout = pa->layout;
 
-  PointerRNA ptr = {{NULL}};
+  PointerRNA ptr = {NULL};
   PropertyRNA *prop = NULL;
   int index = -1;
   uiBut *but = NULL;
@@ -1258,7 +1258,7 @@ static void graph_panel_drivers_popover(const bContext *C, Panel *pa)
 
     /* Populate Panel - With a combination of the contents of the Driven and Driver panels */
     if (fcu && fcu->driver) {
-      ID *id = ptr.id.data;
+      ID *id = ptr.owner_id;
 
       PointerRNA ptr_fcurve;
       RNA_pointer_create(id, &RNA_FCurve, fcu, &ptr_fcurve);